Update exercises.rb
require gems and write test for ex0
first commit for test file
add exercise 1 code and test
write code and test for exercises 2,3,4
add code and test for puts all elements of array
write code and test for updating last element of an array
add code and test to add a string element of an array to that array
correct exercise 5 to check stdout when using puts
add code and test to print out values in an array of hashes
add code and test for determining leap years
change puts to print in exercise 8, code and test for 10, 12
add last test and code with runtime error for passing non-integers
fix error(error) in test for two non-integers